Police in Lebanon have arrested a man under investigation by a U.N. commission probing the assassination of former Prime Minister Rafik Hariri.

Officials in Beirut say Mahmoud Abdel-Al, a member of the pro-Syrian Al-Ahbash Sunni Muslim Orthodox group, was detained early Saturday based on an arrest warrant issued by Lebanese prosecutors.

A U.N. investigative report issued earlier this week said the man telephoned pro-Syrian President Emile Lahoud minutes before Mr. Hariri was killed. A spokesman for Mr. Lahoud has strongly denied the president had been in contact with Mr. Abdel-Al.

Meanwhile, the son of Mr. Hariri, Saad Hariri, called for an international tribunal to punish those responsible for his father's assassination.

In Damascus, Syrian officials dismissed the credibility of the U.N. report, which named senior Syrian security officials and their Lebanese allies as suspects in Mr. Hariri's death.